Making an Anne Frank game while also praising "Adolf Hitler's bolstering of Nazi Germany in the 1930's" is pretty unambiguous, I'd say. Nothing that a random 8chan user couldn't have come up with "for the lulz" of course, but that website has also been associated with violent acts.
Huh. That honestly struck me as irony, given that it’s in conjunction with his grandmother’s departure from Germany. But I do see your point.
Note that the dates may not be accurate; according to a quick bit of genealogical research, his grandmother Paula married his grandfather in Bavaria in 1955 < https://www.genealogy.com/ftm/b/i/s/Robert-S-Bishop/BOOK-000...>. Could also be that she left Germany and then returned for the wedding, of course.
Paula’s mother’s surname appears to have been Ketzler, which doesn’t tell us a ton about ethnic background. Not that it would tell us much about the attacker in any case, even if that was why she left Germany.
Edit: he had at least a bit of 4chan activity, as per his journal.
